The adenoviruses infect many species of the animal world including man. The cytopathogenicity and the oncogenicity of some of these viruses are well documented. In order to obtain further knowledge regarding these viruses, we propose to investigate the biological significance of the phosphorylation of viral proteins. Attempts will be made to domonstrate that some of the proteins ssembled into the viral particle are phosphoproteins by growing adenovirus-assembled into the viral particle are phosphoproteins by growing adenovirus-infected cells in 32-orthophosphate-containing medium. The species of phosphorylated proteins derived from the virus when cultivated in different cell lines will also be analyzed. Since purified adenovirus may be phosphorylated by protein kinase in vitro, it is of interest to investigate whether a similar situation prevails when the virus enters a susceptible host cell. These studies will be conducted with different cell lines, which may either give rise to productive or abortive viral nfection. In vitro phosphorylation of adenviruses will be carried out using protein kinases purified from both infected and uninfected cell lines. The endonucleolytic activity of the viral penton ase following phosphorylation nd dephosphorylation will be ascertained. After phosphorylation of the virion, the susceptibility of the viral nucleic acid to nuclease hydrolysis will be determined.